Universal Mobile Telecommunications System (UMTS) networks have seen an explosive data growth in the past few years and, in the future, are expected to see continuing growth in the Packet Switched (PS) domain. Communication devices can now operate on these robust networks to access data applications (over a PS data bearer) during a voice call (over a circuit switched (CS) voice bearer). This is referred to as multiple radio access bearer (mRAB) calls. Due to the acceleration in demand and use of mobile data applications (e.g., NetFlix, YouTube, Facebook, etc.), the number of short bursty packet sessions are growing exponentially, and most often, these packet sessions are initiated while a user is on a CS voice bearer. Typically, mRAB calls drop at much higher rate than voice only calls. Increased rate in dropped calls causes user frustration and dissatisfaction, and can adversely affect service providers' businesses.
While it's possible to bridge some of the gaps with optimization techniques, conventional systems cannot fully close the inherent radio link budget gap of approximately 1.6-1.9 decibel (dB) for mRAB versus voice only calls. From a competitive positioning point of view, especially with Code Division Multiple Access (CDMA) based technologies, the UMTS Common Pilot Channel (CPICH) coverage presents about a 6 dB advantage over a CDMA pilot coverage. However, in conventional systems, such coverage advantage cannot be leveraged due to coverage degradation during mRAB calls. Moreover, when a PS radio access bearer (RAB) is added to a voice bearer, coverage degradation is mainly due to the lower spreading factor, thus lower spreading gain, or due to the multi-code usage on the uplink (UL).
Conventional systems simply focus on (a) Improving link budget using lower rate speech codecs and lower rate data bearers; (b) Improving the power allocation for signaling radio bearers (SRB); and/or (c) Pro-actively reconfiguring the PS bearer of an mRAB session in order to maintain the speech session. Limitations with solutions mentioned above are as follows: (a) There is an inherent link budget issue that cannot be fully bridged. Wireless carriers have traditionally built their network based on coverage boundaries required to support speech services. When a user has an mRAB connection, the coverage at cell edges will be reduce by approximately 1.6-1.9 dB, which results in a higher probability for session drops under these conditions; (b) 3rd Generation Partnership Project (3GPP) specifies beta parameters that determine the power allocation ratios for the control channel (DPCCH) versus data channel (DPDCH). This is done to ensure support of minimum data rates even at cell borders. Any effort to allocate more power on SRB (DPDCH) compared to SRB (DPCCH) will have adverse consequences for data rate support at cell edge; and (c) Processes involved in reconfiguring an existing mRAB to a speech only bearer will likely put the user equipment (UE) at risk of increased call drops. This is due to the inherent implementation logic of treating radio bearer reconfiguration activities at a higher priority than mobility events that are required to maintain the best link budget for the session.